Advanced Spatial-Division Multiplexed Measurement Systems Propositions—From Telecommunication to Sensing Applications: A Review

Abstract

The concepts of spatial-division multiplexing (SDM) technology were first proposed in the telecommunications industry as an indispensable solution to reduce the cost-per-bit of optical fiber transmission. Recently, such spatial channels and modes have been applied in optical sensing applications where the returned echo is analyzed for the collection of essential environmental information. The key advantages of implementing SDM techniques in optical measurement systems include the multi-parameter discriminative capability and accuracy improvement. In this paper, to help readers without a telecommunication background better understand how the SDM-based sensing systems can be incorporated, the crucial components of SDM techniques, such as laser beam shaping, mode generation and conversion, multimode or multicore elements using special fibers and multiplexers are introduced, along with the recent developments in SDM amplifiers, opto-electronic sources and detection units of sensing systems. The examples of SDM-based sensing systems not only include Brillouin optical time-domain reflectometry or Brillouin optical time-domain analysis (BOTDR/BOTDA) using few-mode fibers (FMF) and the multicore fiber (MCF) based integrated fiber Bragg grating (FBG) sensors, but also involve the widely used components with their whole information used in the full multimode constructions, such as the whispering gallery modes for fiber profiling and chemical species measurements, the screw/twisted modes for examining water quality, as well as the optical beam shaping to improve cantilever deflection measurements. Besides, the various applications of SDM sensors, the cost efficiency issue, as well as how these complex mode multiplexing techniques might improve the standard fiber-optic sensor approaches using single-mode fibers (SMF) and photonic crystal fibers (PCF) have also been summarized. Finally, we conclude with a prospective outlook for the opportunities and challenges of SDM technologies in optical sensing industry.

Recent developments in fibre optic shape sensing

“…In the past few years, SDM has attracted great attention as a new paradigm for fibre optic sensing and communication research [77][78][79]; its sensing applications have been extensively studied in [80].…”

“…Combining SDM technology with FBG allows sensing in parallel spatial channels, for example in MCFs with FBG written single mode cores and in single core multimode fibres (MMF) by modedivision multiplexing [80]. Application of SDM has not been limited to quasi-distributed sensing using FBGs, but also it has been applied for distributed sensing [81].…”

Flexible and Stretchable Photonic Sensors Based on Modulation of Light Transmission

“…Photonics, which is the science and technology about modulation of photons in free space or in matter, influences numerous and diverse fields of modern life . Photonic sensors are widely used and play critical roles in a large variety of fields, such as telecommunication, biotechnology, illumination, imaging, and display . In general, photonic sensors have the following advantages over conventional electronic devices: high sensitivity, low hysteresis, insusceptibility to electromagnetic interference.…”

Signal Analysis, Signal Demodulation and Numerical Simulation of a Quasi-Distributed Optical Fiber Sensor Based on FDM/WDM Techniques and Fabry-Pérot Interferometers

“…This sensor type has received significant research attention and it necessarily applies some multiplexing technique. Several basic multiplexing techniques such as time-division multiplexing, wavelength-, coherence-, frequency-, spatial-, and code-division multiplexing have been proposed, demonstrated and applied over the last 10 years [1,2,3,4,5,6,7,8,9,10]. However, the multiplexing capacities of many of these techniques are limited to only a few sensors due to various factors including cross-talk, limited power budget and wavelength bandwidth.…”